Learn network fundamentals essential for any DevOps specialist, including socket programming, command-line tools, OSI layer protocols, and more.

ce.tar.gz

TCPServer

Fundamentals of DevOps

This module will guide us through the network fundamentals essential for any DevOps specialist. This module starts with different networking concepts, such as the internet, application layer, and transport layer. We'll then move on to learning the basics of socket programming in Python and the network layer. In the end, we'll learn link layer concepts.

Network Fundamentals

## Introduction
There are a few key points to be noted about TCP programs:
- TCP `connect()` calls induce full TCP three-way handshakes! As we saw in [the last chapter](https://www.educative.io/courses/grokking-computer-networking/when-connection-establishment-fails-syn-floods-retransmission), **three-way handshakes can fail and so can `connect()` calls**.

- A **new socket gets created for every new connection** in a TCP architecture.

- **One socket** on TCP servers is dedicated to **continuously listen** for **new** incoming connections. 

- When a connection is successful, that listening socket creates a **new socket exclusively for that connection**.

- When the **connection terminates**, the associated **socket** gets **deleted**. 

- Every socket, and hence **each connection, is identified by the unique 4-tuple: `(local_ip, local_port, remote_ip, remote_port)`**. All incoming TCP packets are examined to see whether their source and destination addresses belong to any such currently connected sockets.

- Unlike UDP, **TCP segments will be delivered as long as the sender and receiver are connected by a path and they are both live**.

- A sending TCP entity might **split TCP segments into packets** and so, receiving TCP entities would have to reassemble them. This is unlikely in our small program but happens all the time in the real world. So we need to take care of when there is data leftover in the buffer to send or to receive after one call.

# Introduction
There are a few key points to be noted about TCP programs:
- TCP `connect()` calls induce full TCP three-way handshakes! As we saw in [the last chapter](https://www.educative.io/courses/grokking-computer-networking/when-connection-establishment-fails-syn-floods-retransmission), **three-way handshakes can fail and so can `connect()` calls**.

- A **new socket gets created for every new connection** in a TCP architecture.

- **One socket** on TCP servers is dedicated to **continuously listen** for **new** incoming connections. 

- When a connection is successful, that listening socket creates a **new socket exclusively for that connection**.

- When the **connection terminates**, the associated **socket** gets **deleted**. 

- Every socket, and hence **each connection, is identified by the unique 4-tuple: `(local_ip, local_port, remote_ip, remote_port)`**. All incoming TCP packets are examined to see whether their source and destination addresses belong to any such currently connected sockets.

- Unlike UDP, **TCP segments will be delivered as long as the sender and receiver are connected by a path and they are both live**.

- A sending TCP entity might **split TCP segments into packets** and so, receiving TCP entities would have to reassemble them. This is unlikely in our small program but happens all the time in the real world. So we need to take care of when there is data leftover in the buffer to send or to receive after one call.

In the last chapter, we studied TCP theory in detail. Now, we'll look at how we can code up TCP programs in Python.

Internet and The OSI Model

The Application Layer

The Transport Layer

An Introduction to Socket Programming with Python

The Network Layer

The Link Layer

Conclusion

A TCP Client-Server Program

Introduction